In general, as amount of information is increased, a magnetic recording medium is demanded which is of mass storage to record a large quantity of information as well as low-priced, and preferably enables so-called high speed access that can read out necessary part within a short time. As an example of such a medium, a high-recording density flexible disc is known, and so-called tracking servo technique, in which a magnetic head accurately scans a narrow track width and generates signals with a high S/N ratio, is playing an important role for realizing such mass storage. In one revolution of disc, a servo tracking signal, an address information signal, a regenerative clock signal and the like are recorded in a predetermined space in so-called pre-format.
The magnetic head is allowed to accurately run over the tracks by reading these pre-format signals and correcting its own position. Recently, the pre-format is formed by recording discs one by one or tracks thereof one by one using an exclusive servo writer.
However, because such a servo writer is very expensive and the formation of pre-format is time-consuming, this process occupies a large part of manufacturing cost and it is desired to reduce cost of process.
Meanwhile, it has been proposed to realize the mass storage by a magnetic transfer method, not by recording tracks one by one in pre-format. For example, such a magnetic transfer method is disclosed in Japanese Unexamined Patent Publication Nos. sho63-183623, hei10-40544, hei10-269566, etc. The magnetic transfer executes transfer of a magnetized pattern corresponding to information (for example, a servo signal) born in a master carrier by applying magnetic field for transfer in the state that the master carrier and slave medium are in close contact with each other, wherein recording can be executed statically without changing the relative position between the master carrier and the slave medium, whereby it is possible to execute accurate pre-format recording and the time needed for the recording is very short.
In order to improve the quality of transfer in said magnetic transfer, it is an important task how to bring the master carrier and slave medium into close contact by uniform force or without any gap. That is, there will be problems in that if the close contact is not assured a region which does not undergo magnetic transfer may be generated, if magnetic transfer is not generated, omission of signals may be caused in the magnetic information transferred onto the slave medium, thereby deteriorating the quality of signal, and if the recorded signals are the servo signals, a satisfactory tracking function can not be obtained and reliability will be lowered.
As a measurement for solving this problem, the inventors have proposed in Japanese Patent Application No. 2001-144296, etc. to provide an adsorption member having a flat surface (holder surface) for adsorbing and holding the rear surface of said master carrier and to bring the master carrier into close contact with the slave medium in the state that the flatness of said master carrier has been enhanced.
This method is described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of main parts showing the transfer state of a magnetic transfer apparatus according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of a holder.
The magnetic transfer apparatus 1 shown in FIGS. 1 and 2 executes simultaneous transfer of both sides by inplane recording technique, in which magnetic field for transfer is applied by magnetic field applying apparatus 5 (electromagnetic devices) located upper and lower sides of a holder 10 which brought master carriers 3 and 4 into confronted close contact with top and bottom sides of a slave medium while rotating the holder 10, so that information born in the master carrier can be magnetically transferred and recorded onto both sides of slave medium 2 at the same time. Herein, the expression “confronted close contact” indicates either close contact state or facing state with a very small gap.
The holder 10 comprises a lower side master carrier 3 for transferring information such as a servo signal onto the lower recording surface of slave medium 2, an upper side master carrier 4 for transferring information such as a servo signal onto the upper recording surface of slave medium 2, a lower side press-contact member (lower side holder) 8 provided with a lower side adsorption member 6 for adsorbing and holding said lower side master medium 3 to correct the flatness thereof, and an upper side press-contact member (upper side holder) 9 provided with an upper side adsorption member 7 (which has a construction same with the lower side adsorption member 6) for adsorbing and holding said lower side master medium 3 to correct the flatness thereof, wherein the master carriers and press-contact members are compressively contacted in the centered state, thereby bringing the lower side master carrier 3 and lower side master carrier 4 into confronted close contact with both surfaces of the slave medium 2.
The slave medium 2 shown in the drawing is a flexible disc consisting of a disc-shaped recording medium 2a with a hub 2b fixed on its center part, wherein the recording medium 2a has recording surfaces formed with magnetic layers on the both surfaces of a disc-shaped base which is formed from a flexible polyethylene terephthalate and the like. This slave medium may be a hard disc.
Said lower side master carrier 3 and upper side master carrier 4 are formed as a disc of circular shape, wherein each of the master carriers have a transfer information-bearing surface formed by a fine uneven pattern on the one surface and is adsorbed by vacuum and held on the lower side adsorption member 6 or upper side adsorption member 7 on the other surface. In order to increase the close contact capability as desired, the lower side master carrier 3 and upper side carrier 4 are provided with fine holes formed through the front and rear surfaces thereof in a position, where the uneven pattern is not formed and where they do not communicate with the adsorption holes in the adsorption members 6 and 7 to be described, to inhale and discharge air from the interface between the closely contacted surfaces.
The lower side adsorption member 6 (and likewise the upper side adsorption member 7) is formed in a disc shape having a size corresponding to that of the master carrier 3, and its surface is formed as an adsorption surface 6a smoothly finished in a planeness having centerline mean roughness Ra in the range of about 0.1˜1.0 μm.
In the adsorption surface 6a, about 25˜100 suction holes are substantially evenly opened, diameters of which do not exceed about 2 mm. Although not shown, these holes are connected to and sucked by a vacuum pump via a adsorption passage way extended from the inside of lower side adsorption member 6 to the outside of lower side press-contact member 8, and vacuum adsorbs the rear surface of master carrier 3 closely contacted onto the adsorption surface 6a to correct the flatness of master carrier 3 to conform to the adsorption surface 6a. 
The lower side press-contact member 8 and upper side press-contact member 9 are disc-shaped and one or both of them is set to be axially movable and performs opening/closing action by an opening/closing mechanism not shown (pressing mechanism, locking mechanism and the like) to be press-contacted with each other in a predetermined pressure. They have flange parts 8a and 9a at the outer circumferences, so that at the time of closing action, the flange parts 8a and 9a will contacts with each other, thereby maintaining the internal parts in the close contact state. The center of lower side press-contact member 8 is provided with a pin 8b for engaging with the center hole of hub 2b of slave member 2 to perform positioning. In addition, the lower side press-contact member 8 and upper side press-contact member 9 are connected to a rotary mechanism (not shown) and rotatably driven in unison.
Said holder 10 executes magnetic transfer for a plurality of slave mediums 2 by the same lower side master carrier 3 and upper side master carrier 4, wherein firstly the lower side master carrier 3 and upper side master carrier 4 are centered on the adsorption surfaces 6a of lower side adsorption member 6 and upper side adsorption member 7, and then respectively maintained thereon by being adsorbed by vacuum.
And, the slave medium 2, which has previously undergone initial magnetization, is centered and set in the opened state where the upper side press-contact member 9 and lower side press-contact member 8 are separated, and then closing operation is performed by approaching the upper side press-contact member 9 and lower side press-contact member 8 to bring the master carriers 3 and 4 into close contact onto both surfaces of slave medium 2. Thereafter, the magnetic field applying apparatus 5 are approached to upper and lower surfaces of holder 10 by moving the upper and lower magnetic field applying apparatus 5 or the holder 10, and the transfer information of lower side master carrier 3 and upper side master carrier 4 is magnetically transferred and recorded onto the recording surfaces of slave medium 2 by applying transfer magnetic field by means of the magnetic field applying apparatus 5 while the holder 10 is being rotated.
In the case of inplane recording, the magnetic field applying apparatus 5 for applying initial magnetic field and transfer magnetic field comprises ring-shaped head electromagnets located upper and lower sides of the slave medium 2, wherein each of the head electromagnets comprises a core having a gap extended, for example, in the radial direction of slave medium 2 and a coil wound around the core, and the magnetic field applying apparatus applies transfer magnetic field generated in the same direction parallel to the track direction from the upper and lower sides. It is possible to arrange the magnetic field applying apparatus 5 only in the one side of the slave medium and it is possible to provide permanent magnetic devices either in the both sides or in the one side of the slave medium. Furthermore, it is possible to rotationally move the magnetic field applying apparatus 5.
In the case of perpendicular recording, electromagnets or permanent magnets having different poles are located in the upper and lower sides of the holder 10 of slave medium 2 and master carrier 3 and magnet field is generated and applied in the vertical direction. When partially applying magnetic field, the magnetic transfer is executed over the entire surface by moving the holder 10 of slave medium 2 and master carrier 3 or the magnetic field.
According to the above aspect, the master carriers 3 and 4 are adsorbed by vacuum onto the adsorption surfaces of adsorption members 6 and 7 of high flatness, respectively, when the master carriers 3 and 4 are brought into close contact with the both surfaces of slave medium 2, whereby it is possible to correct and enhance the flatness of the master carriers. Because the slave medium 2 is compressively contacted and brought into close contact with the upper and lower side flat master carriers 3 and 4 as if it is sandwiched between them, it is possible to bring the slave medium 2 and the master carriers 3 and 4 into close contact with each other evenly all over the entire surfaces without producing any gap between them and to transfer and record magnetized patterns accurately corresponding to the uneven pattern formed in the master carriers 3 and 4 onto the recording surfaces of slave medium 2. Furthermore, because the master carriers 3 and 4 are corrected to be flat prior to being in close contact with the slave medium 2, the master carriers 3 and 4 will not be deformed, no friction will be produced between the slave medium 2 and the master carriers, whereby no damage will be caused and endurance and quality can be enhanced.
However, in the above process, because the slave medium 2 is compressively contacted and brought into close contact with the upper and lower flat master carriers 3 and 4 as if it is sandwiched between them as described in the above, the compression by the holder for retaining the master carriers should be executed evenly.
Therefore, the inventors made a number of holders for getting master carriers and slave medium into close contact and performed magnetic transfer, and as a result, local omission of signals from the transferred signals and deterioration of signal quality were found in some cases. Because it was considered that there was a problem in this close contacting method, the inventors analyzed the shapes and elastic characteristics of the holders. Heretofore, as a method for applying close contact force, the vacuum method (Japanese Unexamined Patent Publication No. sho64-88921) and the like have been proposed.
As can be seen from the experimental examples to be described below in detail, when the vacuum method was used as a method for applying close contact force, although force was uniformly applied all over the holder and thus the force of holder was balanced in the region where the master carriers and slave medium were arranged, it was found that deformation of the holder is generated in the region where the master carriers and the slave medium are not arranged to the extent that the force is to be balanced. In addition, it was found that force was concentrated on the closely contacted disc edge of the master carriers and the slave medium and the close contact force was reduced between the central parts thereof, and thus spacing between the master carrier and the slave medium was increased and inferiority of signal transfer was generated.
The present invention is conceived in consideration of the aforementioned problems in mind. The object of the present invention is to provide a magnetic transfer apparatus which can prevent inferiority of transfer, such as omission of signals, and enhance the quality of transferred signals by bringing the master carrier and slave medium into close contact with each other with uniform force when transfer magnetic field is applied to execute magnetic transfer in the state that a master carrier and a slave medium are brought into confronted close contact and received in a holder.
In addition, in the aforementioned means, said holder 10 was applied with transfer magnetic field by the magnetic field applying apparatus 5. Therefore, there was a problem in that not only the transfer information in the lower side master carrier 3 and upper side master carrier 4 was magnetically transferred and recorded onto the recording surfaces of slave medium 2, but also the holder 10 itself was magnetized depending on its material. If said holder 10 is magnetized, there were some cases in which magnetic field for transfer was inhaled into the holder, effective magnetic field for transfer was deficient, and signal quality was deteriorated.
Driving means for rotating the holder 10 is essential in the aforementioned means. However, as shown in FIG. 1, it was difficult to secure a space for installing the driving means for rotating said holder 10, due to the magnetic field applying apparatus 5, a suction passage to a vacuum pump which is not shown and the like. Furthermore, even if it was possible to secure such a space for installation, the periphery of apparatus became structurally complicated, and problems were arisen in view of maintenance, workability and the like when the aforementioned means was adopted as a general mass production apparatus, although it may be adopted as an experimental apparatus or not.
Furthermore, because magnetic field for transfer was applied to said holder 10 by the magnetic field applying apparatus 5 in the aforementioned means, there were some problems in that depending on the material of this holder 10, it was impossible to obtain sufficient magnetic field intensity, and occasionally the quality of signal for the transfer information of upper and lower master carriers 3 and 4 to be magnetically transferred and recorded onto the recording surface of slave medium 2 was not reached to a required level.
In magnetic transfer, magnetostatic field is applied when signals are recorded in the slave medium. In order to enhance the processing efficiency of magnetic transfer, it is effective to shorten the processing time by increasing magnetic field applying sweep velocity. However, when the processing time was shortened, there were some cases that the quality of signals recorded in the slave medium after transfer was not reached to a level obtained when the magnetic transfer was executed in a normal sweep velocity. After analyzing these phenomena, it was found that if the processing time is shortened, the transfer magnetic field increasing time becomes abrupt, and thus demagnetizing field is generated in the holder formed from a material of low electric resistance and it is impossible to obtain sufficient magnetic field intensity in the closely contacted surfaces of master carrier and slave medium.
The present invention is conceived in consideration of the aforementioned problems. The object of the present invention is to secure the signal quality of transfer signal by defining the specific electric resistance or/and the relative magnetic permeability of holder for retaining the master carrier and the slave medium and applying transfer magnetic field to execute magnetic transfer.
In the aforementioned magnetic transfer apparatus, the inventors also reviewed to accomplish close contact between the master carriers and slave medium by enhancing planeness and flatness of adsorption surfaces of holders in the area that they were contacted with the rear surfaces of master carriers in the upper and lower holders, causing the master carriers to be adsorbed on the basis of those surfaces, and enhancing the flatness of master carriers themselves.
However, when the adsorption surface was formed in high planeness and flatness, there was a problem in that air remained between the adsorption surface and the rear surface of master carriers without being discharged is accumulated and local deformation is generated in the master carriers. In particular, if the number of adsorption holes in the adsorptions surfaces was small or such holes were not formed, said air accumulation is easily produced.
In addition, even if the air accumulation was not generated, there was a problem in that the master carriers are adsorbed onto the adsorption surfaces with the close contact between flat surfaces and the removal of master carriers from the adsorption surfaces for cleaning, exchanging and the like causes deformation of master carriers.
The present invention is conceived in consideration of the aforementioned problems. The object of the present invention is to provide a magnetic transfer apparatus adapted to enhance the quality of transfer signals, in such a way that the flatness of master carriers is made to secure prevention of air accumulation and easiness of removal, thereby improving close contact capability between the slave medium and master carriers.